That would sound very much like he has metastasized prostate cancer, with possible metastases in his spine and maybe elsewhere. There are focused radiation options that might knock down specific metastases. Lots of wisdom and experience here reflected in Mayo Connect. Keep reading and learning. Suggest you consider watching some of the excellent videos produced by Prostate Cancer Research Institute pcri.org. In laymen’s terms.
I’m not a doctor, only a prostate cancer survivor. I think you and your dad should focus on Quality of Life. I would also recommend reading some of the work of Dr. Atul Gawande. He’s a surgeon. One of his books “Being Mortal”. Also an older pbs documentary. One of the things he writes about is how too many people have more surgery in the last six months of their life - sometimes neither extending their life nor giving them good quality of life. Doctors are not skilled saying that the next treatment may have no positive impact.
You could do a visit with the Mayo Clinic and see what they say.
Best of luck to you and your dad.
Remember that caretakers should not neglect their own health of well being while caring for someone else.